Catalyst layers and electrolyzers

ABSTRACT

A catalyst layer for an electrochemical device comprises a catalytically active element and an ion conducting polymer. The ion conducting polymer comprises positively charged cyclic amine groups. The ion conducting polymer comprises at least one of an imidazolium, a pyridinium, a pyrazolium, a pyrrolidinium, a pyrrolium, a pyrimidium, a piperidinium, an indolium, a triazinium, and polymers thereof. The catalytically active element comprises at least one of V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce and Nd. In an electrolyzer comprising the present catalyst layer, the feed to the electrolyzer comprises at least one of CO 2  and H 2 O.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of and claims prioritybenefits from U.S. non-provisional patent application Ser. No.14/704,935 filed on May 5, 2015, now U.S. Pat. No. 9,370,773 issued onJun. 21, 2016, entitled “Ion-Conducting Membranes”. The '935non-provisional application is a continuation-in-part of InternationalApplication No. PCT/US2015/14328, filed on Feb. 3, 2015, entitled“Electrolyzer and Membranes”. The '328 international application claimedpriority benefits, in turn, from U.S. provisional patent applicationSer. No. 62/066,823, filed on Oct. 21, 2014. The '935 non-provisionalapplication is also a continuation-in-part of International ApplicationNo. PCT/US2015/26507, filed on Apr. 17, 2015, entitled “Electrolyzer andMembranes”. The '507 international application also claimed prioritybenefits from the '823 provisional application.

The present application is also related to and claims priority benefitsfrom U.S. provisional patent application Ser. No. 62/066,823, filed onOct. 21, 2014.

The present application is also a continuation-in-part of and claimspriority benefits from U.S. non-provisional patent application Ser. No.14/704,934, filed on May 5, 2015, entitled “Electrochemical Device ForConverting Carbon Dioxide To A Reaction Product”. The '934non-provisional application is a continuation-in-part of the '328international application. The '328 international application claimedpriority benefits, in turn, from the '823 provisional application. The'934 non-provisional application is also a continuation-in-part of the'507 international application. The '507 international application alsoclaimed priority benefits from the '823 provisional application.

The present application is also a continuation-in part of the '507international application, and is also a continuation-in-part of the'328 international application.

The present application is also a continuation-in-part of and claimspriority benefits from U.S. non-provisional patent application Ser. No.15/090,477, filed on Apr. 4, 2016, entitled “Ion-Conducting Membranes”.The '477 application is also a continuation-in-part of the '935application.

The '823 provisional application, the '477, '934 and '935non-provisional applications, and the '328 and '507 internationalapplications are each hereby incorporated by reference herein in theirentirety.

This application is also related to U.S. patent application Ser. No.14/035,935, filed on Sep. 24, 2013, entitled “Devices and Processes forCarbon Dioxide Conversion into Useful Fuels and Chemicals,” now U.S.Pat. No. 9,181,625 issued on Nov. 10, 2015; U.S. patent application Ser.No. 12/830,338, filed on Jul. 4, 2010, entitled “Novel CatalystMixtures”, now abandoned; International Application No. PCT/2011/030098filed on Mar. 25, 2011, entitled “Novel Catalyst Mixtures”; U.S. patentapplication Ser. No. 13/174,365, filed Jun. 30, 2011, entitled “NovelCatalyst Mixtures”; International Patent Application No.PCT/US2011/042809, filed Jul. 1, 2011, entitled “Novel CatalystMixtures”; U.S. patent application Ser. No. 13/530,058, filed Jun. 21,2012, entitled “Sensors for Carbon Dioxide and Other End Uses”;International Patent Application No. PCT/US2012/043651, filed Jun. 22,2012, entitled “Low Cost Carbon Dioxide Sensors”; and U.S. patentapplication Ser. No. 13/445,887, filed Apr. 12, 2012, entitled“Electrocatalysts for Carbon Dioxide Conversion,” now issued as U.S.Pat. No. 9,012,345 issued on Apr. 21, 2015.

STATEMENT OF GOVERNMENT INTEREST

This invention was made, at least in part, with U.S. government supportunder ARPA-E Contracts No. DE-AR-0000345, and DE-AR0000684. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The field of the invention is electrochemistry. The devices, systems andcompositions described involve the electrochemical conversion of carbondioxide into useful products, the electrolysis of water, electric powergeneration using fuel cells and electrochemical water purification.

BACKGROUND OF THE INVENTION

There is a desire to decrease carbon dioxide (CO₂) emissions fromindustrial facilities and power plants as a way of reducing globalwarming and protecting the environment. One solution, known as carbonsequestration, involves the capture and storage of CO₂. Often the CO₂ issimply buried. It would be valuable if instead of simply burying orstoring the CO₂, it could be converted into another product and put to abeneficial use.

Over the years, a number of electrochemical processes have beensuggested for the conversion of CO₂ into useful products. Some of theseprocesses and their related catalysts are discussed in U.S. Pat. Nos.3,959,094; 4,240,882; 4,349,464; 4,523,981; 4,545,872; 4,595,465;4,608,132; 4,608,133; 4,609,440; 4,609,441; 4,609,451; 4,620,906;4,668,349; 4,673,473; 4,711,708; 4,756,807; 4,818,353; 5,064,733;5,284,563; 5,382,332; 5,457,079; 5,709,789; 5,928,806; 5,952,540;6,024,855; 6,660,680; 6,664,207; 6,987,134; 7,157,404; 7,378,561;7,479,570; U.S. Patent App. Pub. No. 2008/0223727; Hori, Y.,“Electrochemical CO2 reduction on metal electrodes”, Modern Aspects ofElectrochemistry 42 (2008), pages 89-189; Gattrell, M. et al. “A reviewof the aqueous electrochemical reduction of CO2 to hydrocarbons atcopper”, Journal of Electroanalytical Chemistry 594 (2006), pages 1-19;and DuBois, D., Encyclopedia of Electrochemistry, 7a, Springer (2006),pages 202-225.

Processes utilizing electrochemical cells for chemical conversions havebeen known for years. Generally, an electrochemical cell contains ananode, a cathode and an electrolyte. Catalysts can be placed on theanode, the cathode, and/or in the electrolyte to promote the desiredchemical reactions. During operation, reactants or a solution containingreactants are fed into the cell. In an electrolytic cell, voltage isthen applied between the anode and the cathode to promote the desiredelectrochemical reaction. Note that the convention for designating thecathode and anode is that the cathode is the electrode at which chemicalreduction occurs. This is different for electrolytic cells (also knownas electrolyzers, devices in which electrical energy is supplied inorder to force a chemical oxidation-reduction reaction) than forgalvanic cells (such as fuel cells and batteries) in which a spontaneouselectrochemical reaction produces electricity in an external circuitduring normal operation. In either case, a chemical species acquireselectrons from the cathode, thus becoming more negative and reducing itsformal oxidation number.

When an electrochemical cell is used as a CO₂ conversion system, areactant comprising CO₂, carbonate or bicarbonate is fed into the cell.A voltage is applied to the cell, and the CO₂ reacts to form newchemical compounds.

One of the issues at present is that to obtain high currents, one needsto run the electrochemical cells for conversion of CO₂ either at lowvoltage efficiency or with continuous additions of co-reactants. Forexample, Schmidt et al., Electrochemical Reduction of CO₂ (available athttp://www.sccer-hae.ch/resources/Talks/08_Krause_Power_to_Value.pdf;last accessed on May 17, 2016) report that over 6 volts need to beapplied to achieve a current of 600 mA/cm². This corresponds to anelectrical efficiency of 21%. Verma, S. et al. Phys. Chem. Chem. Phys.,2016. 18: p. 7075-7084 find that they can achieve 400 mA/cm² at a cellpotential of 3 V (42% electrical efficiency) by continuously supplying 3M KOH to the cell. Unfortunately, if the KOH is recycled, the KOH willreact with CO₂ to form KHCO₃. Verma et al. find that the current dropsto 40 mA/cm² in KHCO₃.

An electrochemical cell for the conversion of CO₂ that achieves (a)reasonable energy efficiencies (at least 40%), (b) reasonable currents(above 150 mA/cm²), and (c) reasonable selectivities (above 50%),without needing to continuously introduce other reactants, wouldrepresent a significant advance in the electrochemical field.

SUMMARY OF THE INVENTION

In one embodiment, an electrolyzer cathode catalyst layer allows highcurrents to be obtained at lower voltages. The catalyst layer containsone or more catalytically active chemical elements and an anionconducting polymer, wherein the ion conducting polymer is comprised ofpositively charged cyclic amine groups.

Preferably the cyclic amine is a one or more of imidazoliums,pyridiniums, pyrazoliums, pyrrolidiniums, pyrroliums, pyrimidiums,piperidiniums, indoliums, triaziniums, and polymers thereof; morepreferably the polymer is one or more of imidazoliums, pyridiniums andpyrazoliums.

Preferably said pyridiniums have no hydrogens directly bound to thenitrogen.

Preferably said imidazoliums, pyrazoliums, pyrrolidiniums, pyrroliums,pyrimidiums, piperidiniums, indoliums, triaziniums, have at least onenitrogen that has no hydrogens directly bound to it.

Preferably such positive charged cyclic amine groups are aromatic.

Preferably the catalytic chemical element is chosen from the list: V,Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W,Re, Ir, Pt, Au, Hg, Al, Si, In, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce,and Nd; more preferably the catalytically active element is chosen fromthe list Pt, Pd, Au, Ag, Cu, Ni, Fe, Sn, Bi, Co, In, Ru and Rh; mostpreferably the catalytically active element is chosen from the list Au,Ag, Cu, Sn, Sb, Bi, and In.

In a preferred embodiment, the weight of the ion conducting polymer inthe catalyst layer is less than 64% of the weight of the catalyticallyactive element. Most preferably the weight of the ion conducting polymerin the catalyst layer is between 1 and 10% of the weight of thecatalytically active element.

In a preferred embodiment the catalyst layer also contains elementalcarbon, most preferably carbon black, such as that available from CabotCorporation, Boston, Mass., USA, under the trade designation VulcanXC-72R.

The catalyst layer can be part of an electrolyzer, fuel cell, battery orsensor.

In a preferred embodiment the catalyst layer is part of an electrolyzer.Electrolysis products may include CO, OH⁻, HCO⁻, H₂CO, (HCO₂)⁻, HCOOH,H₂O₂, CH₃OH, CH₄, C₂H₄, CH₃CH₂OH, CH₃COO⁻, CH₃COOH, C₂H₆, O₂, H₂,(COOH)₂, and (COO⁻)₂.

The feed to the electrolyzer may include at least one of CO₂, HCO₃ ⁻,CO₃ ²⁻ and H₂O.

The catalyst layer may be in electrical contact with the anode orcathode.

In one embodiment, the catalyst layer is part of a CO₂ electrolyzer.Preferably CO₂ is fed into the electrolyzer cathode and water is fedinto the anode.

In a preferred embodiment, the water feed contains an electrolyte,preferably a carbonate, bicarbonate or hydroxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded side view of a fuel cell hardware assemblyincluding a membrane electrode assembly interposed between two fluidflow field plates having reactant flow channels formed in the majorsurfaces of the plates facing the electrodes.

FIG. 2 shows how the voltammograms of a 5 cm² cell change when 0% (200),1% (201), 5% (202), and 10% (203) of PSMIMCl are added to the CO₂electrolyzer cathode catalyst layer, where the percentage is calculatedas the weight of the PSMIMCl divided by the weight of the silver.

FIG. 3 shows how the voltammograms of a 5 cm² CO₂ electrolyzer cellchange when 1% (210), 4% (211), 8% (212), 16% (213) and 32% (214) ofPSTMIMCl are added to the cathode catalyst layer.

FIG. 4 shows how the voltammograms of a 5 cm² CO₂ electrolyzer cellchange when 5x% PSMP is added to the cathode catalyst layer.

FIG. 5 shows how the voltammograms of a 5 cm² CO₂ electrolyzer cellchange when 5% of PSPY is added to the cathode catalyst layer.

FIG. 6. Shows how the voltage (300) and selectivity (301) of a 5 cm² CO₂electrolyzer varies with time when the cell is run at a constant currentof 600 mA/cm².

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

It is understood that the process is not limited to the particularmethodology, protocols and reagents described herein, as these can varyas persons familiar with the technology involved here will recognize. Itis also to be understood that the terminology used herein is used forthe purpose of describing particular embodiments only, and is notintended to limit the scope of the process. It also is to be noted thatas used herein and in the appended claims, the singular forms “a,” “an,”and “the” include the plural reference unless the context clearlydictates otherwise. Thus, for example, a reference to “a linker” is areference to one or more linkers and equivalents thereof known to thoseskilled in the art. Similarly, the phrase “and/or” is used to indicateone or both stated cases can occur, for example, A and/or B includes (Aand B) and (A or B).

Unless defined otherwise, technical and scientific terms used hereinhave the same meanings as commonly understood by one of ordinary skillin the art to which the process pertains. The embodiments of the processand the various features and advantageous details thereof are explainedmore fully with reference to the non-limiting embodiments and/orillustrated in the accompanying drawings and detailed in the followingdescription. It should be noted that the features illustrated in thedrawings are not necessarily drawn to scale, and features of oneembodiment can be employed with other embodiments as the skilled artisanwould recognize, even if not explicitly stated herein.

Any numerical value ranges recited herein include all values from thelower value to the upper value in increments of one unit, provided thatthere is a separation of at least two units between any lower value andany higher value. As an example, if it is stated that the concentrationof a component or value of a process variable such as, for example,size, angle, pressure, time and the like, is, for example, from 1 to 98,specifically from 20 to 80, more specifically from 30 to 70, it isintended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32, andthe like, are expressly enumerated in this specification. For valueswhich are less than one, one unit is considered to be 0.0001, 0.001,0.01 or 0.1 as appropriate. These are only examples of what isspecifically intended and all possible combinations of numerical valuesbetween the lowest value and the highest value are to be treated in asimilar manner.

Moreover, provided immediately below is a “Definitions” section, wherecertain terms related to the articles and process are definedspecifically. Particular methods, devices, and materials are described,although any methods and materials similar or equivalent to thosedescribed herein can be used in the practice or testing of the processor articles.

Definitions

The term “electrochemical conversion of CO₂” as used here refers to anyelectrochemical process where carbon dioxide, carbonate, or bicarbonateis converted into another chemical substance in any step of the process.

The term polymer electrolyte membrane refers to both cation exchangemembranes, which generally comprise polymers having multiple covalentlyattached negatively charged groups, and anion exchange membranes, whichgenerally comprise polymers having multiple covalently attachedpositively charged groups. Typical cation exchange membranes includeproton conducting membranes, such as the perfluorosulfonic acid polymeravailable under the trade designation NAFION from E. I. du Pont deNemours and Company (DuPont) of Wilmington, Del.

The term anion exchange polymer refers to polymers having multiplecovalently attached positively charged groups.

The term “anion exchange membrane electrolyzer” as used here refers toan electrolyzer with an anion-conducting polymer electrolyte membraneseparating the anode from the cathode.

The term “Hydrogen Evolution Reaction” also called “HER” as used hererefers to the electrochemical reaction 2H⁺+2e⁻→H₂.

The term “MEA” as used here refers to a membrane electrode assembly,which typically comprises at least an ion-conducting membrane having ananode layer attached or in close proximity to one face of the membraneand a cathode layer attached or in close proximity to the other side ofthe membrane.

The Term “CV” refers to cyclic voltammetry or cyclic voltammogram.

The term “Millipore water” is water that is produced by a Milliporefiltration system with a resistivity of at least 18.2 megohm-cm.

The term “GC” as used here refers to a gas chromatograph.

The term “imidazolium” as used here refers to a positively chargedligand containing an imidazole group. This includes a bare imidazole ora substituted imidazole. Ligands of the form:

where R₁-R₅ are each independently selected from hydrogen, halogens,linear alkyls, branched alkyls, cyclic alkyls, heteroalkyls, aryls,cyclic aryls, heteroaryls, alkylaryls, heteroalkylaryls, and polymersthereof, such as the vinyl benzyl copolymers described herein, arespecifically included.

The term “pyridinium” as used here refers to a positively charged ligandcontaining a pyridinium group. This includes a protonated bare pyridineor a substituted pyridine or pyridinium. Ligands of the form

where R₆-R₁₁ are each independently selected from hydrogen, halogens,linear alkyls, branched alkyls, cyclic alkyls, heteroalkyls, aryls,cyclic aryls, heteroaryls, alkylaryls, heteroalkylaryls, and polymersthereof, such as the vinyl benzyl copolymers described herein, arespecifically included.

The term “pyrazoliums” as used here refers to a positively chargedligand containing a pyrazolium group. This includes a bare pyrazolium ora substituted pyrazolium. Ligands of the form

where R₁₆-R₂₀ are each independently selected from hydrogen, halogens,linear alkyls, branched alkyls, cyclic alkyls, heteroalkyls, aryls,cyclic aryls, heteroaryls, alkylaryls, heteroalkylaryls, and polymersthereof, such as the vinyl benzyl copolymers described herein, arespecifically included.

The term “phosphonium” as used here refers to a positively chargedligand containing phosphorous. This includes substituted phosphorous.Ligands of the form:P⁺(R₁₂R₁₃R₁₄R₁₅)where R₁₂-R₁₅ are each independently selected from hydrogen, halogens,linear alkyls, branched alkyls, cyclic alkyls, heteroalkyls, aryls,cyclic aryls, heteroaryls, alkylaryls, heteroalkylaryls, and polymersthereof, such as the vinyl benzyl copolymers described herein, arespecifically included.

The term “positively charged cyclic amine” as used here refers to apositively charged ligand containing a cyclic amine. This specificallyincludes imidazoliums, pyridiniums, pyrazoliums, pyrrolidiniums,pyrroliums, pyrimidiums, piperidiniums, indoliums, triaziniums, andpolymers thereof, such as the vinyl benzyl copolymers described herein.

The term “electrochemical device” as used here refers to a devicecapable of either generating electrical energy from chemical reactionsor facilitating chemical reactions through the introduction ofelectrical energy. Batteries, fuel cells, electrolyzers, andelectrochemical reactors are specifically included.

The term “vinyl benzyl derivatives” as used here refers to a chemical ofthe form.

or polymers thereof where X is hydrogen, halogens, linear alkyls,branched alkyls, cyclic alkyls, heteroalkyls, aryls, cyclic aryls,heteroaryls, alkylaryls, heteroalkylaryls, imidazoliums, pyridiniums,pyrazoliums, pyrrolidiniums, pyrroliums, pyrimidiums, piperidiniums,indoliums, or triaziniums. Polymers thereof, such as the vinyl benzylcopolymers described herein, are specifically included.

Specific Description

One embodiment of the advance is an electrolyzer cathode catalyst layerthat improves the output of a CO₂ electrolyzer.

FIG. 1 illustrates a fuel cell hardware assembly 30, which includes amembrane electrode assembly 32 interposed between rigid flow fieldplates 34 and 36, the flow fields typically being formed of graphite ora graphite composite material. Membrane electrode assembly 32 consistsof a polymer electrolyte (ion exchange) membrane 42 interposed betweentwo electrodes, namely, anode 44 and cathode 46. Anode 44 and cathode 46are typically formed of porous electrically conductive sheet material,preferably carbon fiber paper, and have planar major surfaces.Electrodes 44 and 46 have a thin layer of catalyst material disposed ontheir major surfaces at the interface with membrane 42 to render themelectrochemically active.

A distinguishing feature here is the addition of anion conductingpolymers to the catalyst layer to improve the cell output.

There are many previous descriptions of catalyst layers forelectrochemical cells. Patents include U.S. Pat. Nos. 5,234,777;5,869,416; 6,156,449; 6,696,382; 6,800,391; 6,844,286; 7,364,813;7,754,369; 7,754,369; 7,855,160; 7,906,452; 8,198,206; 8,481,231;8,940,460; 9,127,182; and 9,160,008; U.S. Pat. App. Pub. Nos.2002/0034674; 2002/0098405; 2004/0023104; 2004/0107869; 2005/0151121;2006/0110631; 2008/0248944; 2010/0196785; 2010/0285951; 2011/0003071;2011/0166009; 2011/0262828; 2012/0094210; 2012/0148936; 2012/0171583.2012/0196741; 20120/258381; 2013/0260278; 2014/0162170; 2014/0220474;and 2014/0228200; and International Publication Nos. WO2015/092371 andWO2015/124250. However, in most cases acidic polymers such asperfluorosulfonic acids, including those available from DuPont under thetrade designation Nafion, are used. Acidic polymers substantiallydecrease the selectivity of CO₂ electrolyzers, so they are typically notuseful in practical CO₂ electrolyzers.

There are a few reports of anionic fuel cells with anion conductingpolymers having multiple covalently attached positively charged groupsin their catalyst layer. See for example U.S. Pat. Nos. 3,403,054;7,785,750; and 8,257,872; U.S. Pat. App. Pub. No. 20150171453;International Publication Nos. WO/2013/0137011 and WO/2012/078513; andMatsuoka et al., Journal of Power Sources, Volume 150, 4 Oct. 2005,pages 27-31. However, these authors use polymers containing amines ofthe form:

where the bond on the left is an attachment to the polymer and the Rgroups are either, hydrogens, methyls or ethyls, not positively chargedcyclic amines such as imidazolium or pyrazolium. Si et al. (J. Mater.Chem. A, 2014. 2: p. 4413-4421.), Yan et al (J. Power Sources, 2014.250: p. 90-97.), and Schauer et al. (the Schauer paper) Journal ofApplied Polymer Science, 2015. 132: 42581, disclose imidazolefunctionalized poly(arylene ether sulfone) and poly(ether ketone)polymers, but Schauer et al. FIG. 2 shows that these polymers areunstable under alkaline conditions so they are unsuitable for use inalkaline electrolyzers.

U.S. Pat. No. 6,841,285, notes that, “Thus imidazole and pyrazole mayact as both hydrogen donors and acceptors in proton conductionprocesses. While these compounds may show increased conductivity withinmembrane systems, it is unlikely that they are suitable for use withinthe fuel cell environment. For example, a recent study by C. Yang etal., Journal of Power Sources 103:1, 2001, reports that imidazoleimpregnated membranes poisoned the catalysts.”

Note that imidazole and pyrazole would be protonated under the acidicconditions in U.S. Pat. No. 6,841,285 thus forming imidazolium andpyrazolium ions, so that the implication of the '285 patent is thatimidazoliums and pyrazoliums should not be used in a catalyst layer.

The present work shows that in contrast to the implication in the '285patent, polymers containing imidazoliums, pyrazoliums and pyridiniumsenhance the performance of a CO₂ electrolyzer.

The catalyst layer can also include at least one Catalytically ActiveElement. “Catalytically Active Element” as used here refers to achemical element that can serve as a catalyst for the electrochemicalconversion of CO₂ or another species of interest in a desired reaction.In particular, the device can include one or more of the followingCatalytically Active Elements: V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb,Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Tl,Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd. Research has established thatPt, Pd, Au, Ag, Cu, Ni, Fe, Sn, Bi, Co, In, Ru and Rh perform well, withAu, Ag, Cu, Sn, Sb, Bi, and In perform especially well.

Embodiments of the present invention also include the addition ofelectrically conductive species to the catalyst layer, with carbon beinga conductive preferred component.

Without further elaboration, it is believed that persons familiar withthe technology involved here using the preceding description can utilizethe invention to the fullest extent. The following examples areillustrative only, and are not meant to be an exhaustive list of allpossible embodiments, applications or modifications of the invention.

Specific Example 1

The objective of this example is to show that in contrast to theindication in U.S. Pat. No. 6,841,285, the addition of polymerscontaining imidazoliums to the catalyst layer enhances the performanceof a CO₂ electrolyzer.

A copolymer, which is designated here as PSMIM (Cl), was preparedfollowing the synthetic route in patent application Ser. No. 14/704,935.“PSMIM” refers to a co-polymer of polystyrene and polyl-(p-vinylbenzyl)-3-methyl-imidazolium:

where X⁻ is an anion, m>0 and n>0.

The inhibitor-free styrene was prepared by passing styrene(Sigma-Aldrich, Saint Louis, Mo.) through the tert-butylcatechol (TBC)inhibitor remover (Sigma-Aldrich 311340). In general, 40 ml of removeris sufficient to yield 50 ml of clear, inhibitor free styrene. InhibitorTBC in 4-vinylbenzyl chloride (4-VBC) was removed by the same inhibitorremover in a similar fashion.

Poly(4-vinylbenzyl chloride-co-styrene) was then synthesized by heatinga solution of inhibitor-free styrene (Sigma-Aldrich) (36.139 g, 350mmol) and 4-vinylbenzyl chloride (Sigma-Aldrich) (29.7272 g, 190 mmol)in chlorobenzene (Sigma-Aldrich) (45 ml) at 60-65° C. in an oil bath forapproximately 20 hours under argon gas with AIBN(α,α′-Azoisobutyronitrile, Sigma-Aldrich) (0.5927 g, 0.90 wt % based onthe total monomers' weight) as initiator. The copolymer was precipitatedin CH₃OH (methanol) and dried under vacuum.

“Polystyrene methyimidazolium chloride” (PSMIM) was synthesized byadding 1-methylimidazole (Sigma-Aldrich) (2.8650 g, 034.9 mmol), whichis an alkylimidazole, to the solution of the poly(4-VBC-co-St) (5.0034g, 19.4 mmol) in anhydrous N,N-Dimethylformamide (DMF) (Sigma-Aldrich)(30 mL). The mixture was then stirred at around 30° C. for around 50hours to form a PSMIM solution.

“4-VBC-co-St” or “poly(4-vinylbenzyl chloride co-styrene)” as used hererefers to a co-polymer of styrene and 4-vinylbenzyl chloride:

PSMIM-DVB was synthesized starting with poly(4-vinylbenzyl chlorideco-styrene.) 1-methylimidazole (Sigma-Aldrich) (3.912 g, 47.7 mmol) wasadded in a 250 ml 3-neck round bottom flask to the solution of thepoly(4-VBC-co-St) (15.358 g, 59.8 mmol) in anhydrousN,N-Dimethylformamide (DMF) (Sigma-Aldrich) (105 mL). 0.22 ml of adivinylbenzene (DVB) in DMF solution (DVB concentration=0.0083 g/ml) wascarefully added through a pipette to the mixture with continual magneticstirring. After this, 0.22 ml of AIBN-DMF solution (AIBNconcentration=0.0083 g/ml) was added to the mixture in a similarfashion. The reaction was then kept under nitrogen atmosphere at 50° C.for about 60 hours. PSMIM-DVB was obtained as a white powder afterpurification by precipitation into diethyl ether.

Membranes were prepared by casting the PSMIM-DVB solution prepared abovedirectly onto a flat glass surface. The thickness of the solution on theglass was controlled by a film applicator (MTI Corporation, Richmond,Calif.) with an adjustable doctor blade. The membranes were then driedin a vacuum oven in the following step wise fashion. They were firstkept at 80° C. for 120 minutes, then at 100° C. for 60 minutes, at 120°C. for 30 minutes and finally at 150° C. for 60 minutes. Chloride ionsin the membranes were removed by soaking the membranes in 1 M KOHsolution for 24 hours or longer.

The cathode layer in Specific Example 1 was prepared as follows. Silverink was made by mixing 100 mg of silver nanoparticles (20-40 nm, 45509,Alfa Aesar, Ward Hill, Mass.), 5 mg porous carbon (Vulcan XC-72R, FuelCell Earth, Woburn, Mass.) and different amounts of PSMIM-Cl in 3 ml ofethanol (459844, Sigma-Aldrich, St. Louis, Mo.). The mixture was thensonicated for 10 minutes. The silver ink was painted onto a gasdiffusion layer (Sigracet 35 BC GDL, Ion Power Inc., New Castle, Del.)covering an area of 6 cm×6 cm. The electrode was immersed in 1 M KOH forat least 1 hour so that PSMIM-Cl converted by ion exchange to PSMIM-OH.Then the electrode was cut into 2.5 cm×2.5 cm sections for cell testing.

The anode in Specific Example 1 was prepared as follows: 100 mg of IrO₂(43396, Alfa Aesar, Ward Hill, Mass.) was dispersed in the mixture of 1ml of deionized water, 2 ml of isopropanol (3032-16, Macron FineChemicals, Avantor Performance Materials, Center Valley, Pa.) and 0.1 mlof 5 wt. % poly-tetrafluoroethylene (PTFE) dispersion (665800,Sigma-Aldrich, St. Louis, Mo.). The mixture was sonicated for 10 minusing a water bath sonicator. The ink was painted onto 6 cm×6 cm ofcarbon fiber paper (Toray Paper 120, Fuel Cell Earth, Woburn, Mass.).The actual IrO₂ loading was about 2 mg/cm². The electrode was cut into 3cm×3 cm sections for cell testing.

The membrane was sandwiched between the anode and the cathode with themetal-containing layers on the anode and cathode facing the membrane,and the whole assembly was mounted in a Fuel Cell Technologies 5 cm²fuel cell hardware assembly with serpentine flow fields.

CO₂ humidified at 25° C. was fed into the cathode flow field at a rateof 20 sccm, and 10 mM KHCO₃ was fed into the anode flow field. Thecyclic voltammograms were collected by scanning the cell potential from1.2 to 3.0 V. All of the scans were made at room temperature andatmospheric pressure.

FIG. 2 shows the results. Plot 200 is a base case with no PSMIM in thecathode catalyst layer ink. Notice that the current increases when PSMIMis added to the catalyst layer in a later sample, such that the PSMIMweight is 1% of the weight of the silver (plot 201). Further increasesin the current are seen as the PSMIM concentration is increased so thatthe PSMIM weight is 5% of the weight of the silver (plot 202). Thenthere is a small decrease when the weight of the PSMIM is increased to10% of the weight of the silver (plot 203). A decrease in theselectivity of the reaction was observed.

A run in which the PSMIM weight was 20% of the weight of the silver wasalso performed. The cell showed a small current, but analysis of theexit stream did not show significant CO₂ conversion.

These results demonstrate that the addition of an ionomer containing animidazolium enhances the performance of a CO₂ electrolyzer, in contrastto the findings in U.S. Pat. No. 6,841,285.

Specific Example 2

The objective of this example is to show that in contrast to thefindings in U.S. Pat. No. 6,841,285, the addition of polymers containingtetra-methyl-imidazolium to the catalyst layer enhances the performanceof a CO₂ electrolyzer.

Preparation of PSTMIM: poly(4-vinylbenzyl chloride-co-styrene) wasprepared as in Specific Example 1. Tetra-methyl-imidazolium (TCI) (5.934g) was added to the solution of the poly(4-VBC-co-St) (10 g) inanhydrous N,N-Dimethylformamide (DMF) (Sigma-Aldrich) (85 mL). Themixture was stirred at 30-35° C. for around 60 hours. PSTMIM wasobtained as white solid particles after purification by precipitationinto diethyl ether. PSTMIM refers to a material that contains aco-polymer of styrene and l-(p-vinylbenzyl)-tetra-methyl-imidazolium.

The cathode in Specific Example 2 was prepared as follows. Silver inkwas made by mixing 100 mg of silver nanoparticles (20-40 nm, 45509, AlfaAesar, Ward Hill, Mass.), 5 mg porous carbon (Vulcan XC-72R, Fuel CellEarth, Woburn, Mass.) and different amounts of PSTMIM-Cl in 3 ml ofethanol (459844, Sigma-Aldrich, St. Louis, Mo.). The mixture was thensonicated for 10 minutes. The silver ink was painted onto a gasdiffusion layer (Sigracet 35 BC GDL, Ion Power Inc., New Castle, Del.)covering an area of 6 cm×6 cm. The electrode was immersed in 1 M KOH forat least 1 hour so that PSTMIM-Cl converted to PSTMIM-OH. Then theelectrode was cut into 2.5 cm×2.5 cm for cell testing.

The anode in specific example 2 was the same as in Specific Example 1and the cell was tested as in Specific Example 1.

FIG. 3 shows the voltammograms measured at varying PSTMIM content.Notice that the current is higher than the base case (plot 200) in FIG.2 when PSTMIM is added to the catalyst later so that the PSTMIM weightis 1% of the weight of the silver (plot 210). Further increases in thecurrent are seen as the PSTMIM concentration is increased so that thePSTMIM weight is 4% of the weight of the silver (plot 211). Then thereis a small decrease when the weight of the PSTMIM is increased to 8% ofthe weight of the silver (plot 212). The performance continues todecrease when the weight of the PSTMIM is 16% of the weight of thesilver (plot 213), but the cell current is still higher than the basecase in FIG. 2 (plot 200). The performance is lower than the base casein FIG. 2 (plot 200) when the weight of the PSTMIM is 32% of the weightof the silver (plot 214), but the cell current is still significant.

A run in which the PSTMIM weight was 64% of the weight of the silver wasalso performed. The cell showed a small current, but analysis of theexit stream did not show significant CO₂ conversion. These resultsdemonstrate that the addition of an ionomer containingtetra-methyl-imidazolium enhances the performance of a CO₂ electrolyzer,in contrast to the findings in the '285 patent.

Specific Example 3

The objective of this example is to show that in contrast to thefindings in U.S. Pat. No. 6,841,285, the addition of polymers containingpyridiniums to the catalyst layer changes the performance of a CO₂electrolyzer but does not poison it.

Preparation of PSMP: poly(4-vinylbenzyl chloride co-styrene) wasprepared as in Specific Example 1. Pyridine (Sigma-Aldrich) (0.318 g,4.68 mmol) was added to the solution of the poly(4-VBC-co-St) (1 g, 3.89mmol) in anhydrous N,N-Dimethylformamide (DMF) (Sigma-Aldrich) (8 mL).The mixture was stirred at room temperature for 60 hours, and PSMP wasobtained as a white solid after purification by precipitation intodiethyl ether. PSMP refers to a material that contains a co-polymer ofstyrene and l-(p-vinylbenzyl)-pyridinium.

The cathode in Specific Example 3 was prepared as follows. Silver inkwas made by mixing 100 mg of silver nanoparticles (20-40 nm, 45509, AlfaAesar, Ward Hill, Mass.), 5 mg porous carbon (Vulcan XC-72R, Fuel CellEarth, Woburn, Mass.) and different amounts of PSMP-Cl in 3 ml ofethanol (459844, Sigma-Aldrich, St. Louis, Mo.). The mixture was thensonicated for 10 minutes. The silver ink was painted onto a gasdiffusion layer (Sigracet 35 BC GDL, Ion Power Inc., New Castle, Del.)covering an area of 6 cm×6 cm. The electrode was immersed in 1 M KOH forat least 1 hour so that PSMP-Cl was converted to PSMP-OH. Then theelectrode was cut into 2.5 cm×2.5 cm sections for cell testing.

The anode in Specific Example 3 was the same as in Specific Example 1and the cell was tested as in Specific Example 1.

FIG. 4 shows the voltammograms measured when the weight of the PSMP was5% of the weight of the silver. Notice that the current is considerablyabove the base case (200) in FIG. 2. These results demonstrate that theaddition of an ionomer containing a pyridinium enhances the performanceof a CO₂ electrolyzer, in contrast to the findings in the '285 patent.

Specific Example 4

The objective of this example is to show that in contrast to thefindings in the '285 patent, the addition of polymers containingpyrazoliums to the catalyst layer enhances the performance of a CO₂electrolyzer.

Preparation of PSPZ: poly(4-vinylbenzyl chloride co-styrene) wasprepared as in Specific Example 1. Pyrazole (Sigma-Aldrich) (0.593 g,4.67 mmol) was added to the solution of the poly(4-VBC-co-St) (1 g, 3.89mmol) in anhydrous N,N-Dimethylformamide (DMF) (Sigma-Aldrich) (8 mL).The mixture was stirred at room temperature for 60 hours and thisPSPY-DMF was accordingly further diluted for use as the ionomer. PSPYrefers to a material that contains a co-polymer of styrene andl-(p-vinylbenzyl)-pyrazolium ionomers.

The anode in Specific Example 4 was the same as in Specific Example 1and the cell was tested as in Specific Example 1.

FIG. 5 shows a voltammogram measured when the weight of the PSPY was 5%of the weight of the silver. Notice that the current is considerablyabove the base case (200) in FIG. 2. These results demonstrate that theaddition of an ionomer containing a pyrazolium enhances the performanceof a CO₂ electrolyzer, in contrast to the findings in the '285 patent.

Specific Example 5

The objective of this example is to show that the addition of a PSMIM tothe cathode of a CO₂ electrolyzer also improves the steady stateperformance of the electrolyzer.

The anode and cathode for this test were synthesized as in SpecificExample 1. The weight of the PSMIM in the cathode layer was 2% of theweight of the silver.

A PSTMIM-DVB membrane was used in this experiment. The preparation ofthe PSTMIM-DVB membrane is as follows: Poly(4-vinylbenzyl chlorideco-styrene) was formed as in specific example 1. Tetramethylimidazole(TMIM) (TCI) (4.05 g, 32.6 mmol) was added in a 250 ml 3-neck roundbottom flask to the solution of the poly(4-VBC-co-St) (10 g, 38.9 mol)in anhydrous N,N-Dimethylformamide (DMF) (Sigma-Aldrich) (73 mL). Afterthe TMIM was thoroughly dissolved within this reaction mixture, 1 mL ofa DVB-DMF solution (DVB concentration=0.052 g/ml) was carefully addedthrough a pipette to the mixture with continual magnetic stirring. Afterthis, 1 ml of AIBN-DMF solution (AIBN concentration=0.00135 g/ml) wasadded to the mixture in a similar fashion. The reaction was then keptunder nitrogen atmosphere at 50° C. for about 60 hours. PSTMIM wasobtained as a white powder after purification by precipitation intodiethyl ether. A PSTMIM-DVB membrane was then formed as in SpecificExample 1.

The cell was assembled and tested as in Specific Example 1.

FIG. 6 shows how the voltage and selectivity varied with time when thecell was held at a fixed current of 3 amps (600 mA/cm²). Notice that thecell is producing 600 mA/cm² at 3.3 volts. GC analysis showed that thecell was converting CO₂ to CO with over 95% selectivity to CO. Bycomparison, the Schmidt paper (referred to above, available athttp://www.sccer-hae.ch/resources/Talks/08_Krause_Power_to_Value.pdf;last accessed on May 17, 2016) requires over 6 volts to reach the samecurrent. Consequently, our cell would only need about half as muchenergy as Schmidt et al.'s to convert CO₂ at a rate corresponding to 600mA/cm². The results are stable. The loss of performance reported in theSchauer paper is not seen.

More generally, notice that Specific Examples 1, 2, 3, 4 and 5 show thatadding three different ion conducting polymer containing positivelycharged cyclic amine groups to the catalyst layer in a CO₂ electrolyzerenhance the performance of a CO₂ electrolyzer, in contrast to thefindings in the '285 patent. This observation is believed to be general.That is, adding ion conducting polymer containing positively chargedcyclic amine groups can enhance the performance of electrolyzers andother devices.

While particular elements, embodiments and applications of the presentinvention have been shown and described, it will be understood that theinvention is not limited thereto since modifications can be made bythose skilled in the art without departing from the scope of the presentdisclosure, particularly in light of the foregoing teachings.

The examples given above are merely illustrative and are not meant to bean exhaustive list of all possible embodiments, applications ormodifications of the present electrochemical device. Thus, variousmodifications and variations of the described articles, methods andsystems of the invention will be apparent to those skilled in the artwithout departing from the scope and spirit of the invention. Althoughthe invention has been described in connection with specificembodiments, it should be understood that the invention as claimedshould not be unduly limited to such specific embodiments. Indeed,various modifications of the described modes for carrying out theinvention which are obvious to those skilled in the chemical arts or inthe relevant fields are intended to be within the scope of the appendedclaims.

What is claimed is:
 1. An electrolyzer comprising a catalyst layercomprising a catalytically active element interspersed with an ionconducting polymer, wherein said catalytic active element is selectedfrom the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo,Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Tl, Pb,Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd; and wherein said ion conductingpolymer comprises: a copolymer of styrene, the copolymer furthercomprising positively charged cyclic amine groups, the electrolyzerhaving a reactant stream input, wherein the reactant stream to theelectrolyzer comprises at least one of CO₂ or H₂O.
 2. The electrolyzerof claim 1, the electrolyzer having an anode and a cathode, wherein saidcatalyst layer is in direct electrical contact with at least one of theanode or the cathode.
 3. The electrolyzer of claim 2, wherein the CO₂ isfed into the cathode.
 4. The electrolyzer of claim 2, wherein saidcatalyst layer is in direct electrical contact with the cathode.
 5. Theelectrolyzer of claim 2, wherein water is fed into the anode.
 6. Theelectrolyzer of claim 5, wherein the water feed further comprises anelectrolyte.
 7. The electrolyzer of claim 6, wherein the electrolyte isat least one of a carbonate, a bicarbonate or a hydroxide.
 8. Anelectrolyzer comprising a catalyst layer comprising a catalyticallyactive element interspersed with an ion conducting polymer, wherein saidcatalytic active element is selected from the group consisting of V, Cr,Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re,Ir, Pt, Au, Hg, Al, Si, In, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, andNd; and wherein said ion conducting polymer comprises: a terpolymer ofstyrene, vinylbenzyl-R_(s) wherein R_(s) is a positively charged cyclicamine group, and vinylbenzyl-R_(x), wherein R_(x) is at least oneconstituent selected from the group consisting of Cl, OH, and a reactionproduct between an OH or Cl and a reactant other than an amine, andwherein the total weight of the vinylbenzyl-R_(x) groups is at least 1%of the total weight of the terpolymer, the electrolyzer having areactant stream input, wherein the reactant stream to the electrolyzercomprises at least one of CO₂ or H₂O.
 9. The electrolyzer of claim 8,the electrolyzer having an anode and a cathode, wherein said catalystlayer is in direct electrical contact with at least one of the anode orthe cathode.
 10. The electrolyzer of claim 9, wherein the CO₂ is fedinto the cathode.
 11. The electrolyzer of claim 9, wherein said catalystlayer is in direct electrical contact with the cathode.
 12. Theelectrolyzer of claim 9, wherein water is fed into the anode.
 13. Theelectrolyzer of claim 12, wherein the water feed further comprises anelectrolyte.
 14. The electrolyzer of claim 13, wherein the electrolyteis at least one of a carbonate, a bicarbonate or a hydroxide.